Landing string

ABSTRACT

A landing string for use in deploying equipment between a surface vessel and a subsea well comprises a separation assembly configured to permit relative movement of upper and lower regions of the landing string upon exposure to a predetermined load.

FIELD OF THE INVENTION

The present invention relates to a landing string, and in particular to a landing string which includes protection against excessive loading.

BACKGROUND TO THE INVENTION

Landing strings are used in the oil and gas industry for through-riser deployment of equipment, such as completion architecture, well testing equipment, intervention tooling and the like into a subsea well from a surface vessel. When in a deployed configuration the landing string extends between the surface vessel and the wellhead, for example a wellhead Blow Out Preventor (BOP). While deployed the landing string provides many functions, including permitting the safe deployment of wireline or coiled tubing equipment through the landing string and into the well, providing the necessary primary well control barriers and permitting emergency disconnect while isolating both the well and landing string.

Wireline or coiled tubing deployment may be facilitated via a lubricator valve which is located proximate the surface vessel, for example below a rig floor.

Well control and isolation in the event of an emergency disconnect is provided by a suite of valves which are located at a lower end of the landing string, normally positioned inside the central bore of the BOP. This valve suite includes a lower valve assembly called the subsea test tree (SSTT) which provides a safety barrier to contain well pressure, and an upper valve assembly called the retainer valve which isolates the landing string contents and can be used to vent trapped pressure from between the retainer valve and SSTT. A shear sub component extends between the retainer valve and SSTT which is capable of being sheared by the BOP to permit an emergency disconnect. However, this ability to provide an emergency disconnect is limited only to when the landing string is fully deployed and the shear sub component is appropriately positioned within the BOP.

The landing string must be capable of accommodating the significant in-service loadings, such as its own weight, the global tension from a supported lower string (e.g., a test string, completion or the like), bending loads, and the like. As the industry continues to move into fields with increasing formation and water depths, the resulting structural demands on the landing string also become more extreme. For example, landing string global tension requirements far in excess of 4.5 MN (1,000,000 lbf) are typical.

Furthermore, the surface vessel and associated equipment, such as hang-off equipment, must also be capable of supporting the weight of the landing string and its payload. In some circumstances the supported weight and loading may exceed the capacity of the surface vessel and associated equipment. This could result in damage to the surface vessel equipment, and possibly compromise wellbore containment.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a landing string for use in deploying equipment between a surface vessel and a subsea well, comprising a separation assembly configured to permit relative movement of upper and lower regions of the landing string upon exposure to a predetermined load.

The upper region of the landing string may be defined as that region which, in use, extends between the separation assembly and a vessel. The lower region of the landing string may be defined as that region which, in use, extends between the separation assembly and equipment to be, or being, deployed.

Although the terms “upper” and “lower” have been used, it should be understood that these are not intended to limit the precise orientation and geometry of the landing string. For example, some or all of the landing string may be utilised in a substantially vertical orientation, inclined orientation, horizontal orientation or the like.

In use, the separation assembly may permit a controlled relative movement of the upper and lower regions of the landing string at or around the predetermined load. This controlled permission of relative movement will therefore be provided at a predetermined location, i.e., the location of the separation assembly.

The separation assembly may provide protection to the landing string against excessive loading. The separation assembly may provide protection to a surface vessel and/or any associated equipment, such as lifting or handling equipment or the like, against excessive loading. The separation assembly may provide protection to equipment being deployed, or previously deployed, against excessive loading.

Permitting controlled relative movement of the upper and lower regions of the landing string may assist to control transmission of load between said regions and along the landing string. For example, such relative movement upon exposure to a predetermined load may minimise or completely prevent the transmission of load between said regions of the landing string. This may assist to protect the landing string, a surface vessel and/or any supported equipment from excessive loading and forces.

The provision of a separation assembly which itself is configured to permit relative movement between upper and lower regions upon exposure to a predetermined load may offer significant advantages over prior art systems. For example, the present invention does not rely on specific alignment and interaction with external equipment, such as a BOP, to effect such relative movement, for example separation. Instead, the separation assembly may permit relative movement of upper and lower regions of the landing string at any time during use, for example during deployment between a vessel and a subsea well, while deployed, during retrieval or the like.

The predetermined load may comprise a predetermined axial load. The predetermined load may comprise a predetermined tensile load. Tensile loading may be created by the weight of the landing string, for example the lower region of the landing string, and any supported equipment. Tensile loading may be applied via any handling or lifting equipment associated with a vessel, and/or any regions of interaction between the landing string and/or supported equipment with adjacent structure, such as wellbore structure and the like.

The predetermined load may comprise a compressive load.

The predetermined load may comprise a torsional load.

The predetermined load may comprise a pressure induce load.

The separation assembly may define a linkage or connection between the upper and lower regions of the landing string.

The separation assembly may define a weak link or connection arrangement. That is, the separation assembly may define a structurally weak region relative to the remainder of the landing string. In this way, any reaction to loading may be focused at the separation assembly.

The separation assembly may define a rigid connection between the upper and lower regions of the landing string prior to exposure to the predetermined load. Such a rigid connection may be intended to prevent any relative movement between the upper and lower regions until exposure to the predetermined load.

The separation assembly may be configured to permit relative movement between the upper and lower regions upon exposure to the predetermined load while still defining a connection therebetween. In such an arrangement the separation assembly may define a compliant connection between the upper and lower regions following exposure to the predetermined load. Such compliance may be provided to retain the upper and lower regions of the landing string in general engagement with each other while minimising the load transference between said regions.

The separation assembly may be configured to damp relative movement between the upper and lower regions of the landing string following exposure to the predetermined load. The separation assembly may comprise a fluid damping arrangement, such as a piston arrangement, nozzle arrangement or the like.

The separation assembly may be configured to permit complete separation of the upper and lower regions of the landing string. Such an arrangement may completely mechanically isolate the upper and lower regions.

The separation assembly may be configured to permit complete separation of the upper and lower regions from a rigid connection configuration upon exposure to the predetermined load. The rigid connection configuration may be a configuration in which the separation assembly provides a rigid connection between the upper and lower regions of the landing string.

The separation assembly may be configured to permit complete separation of the upper and lower regions from a compliant connection configuration upon exposure to a predetermined load. The compliant connection configuration may be a configuration in which the separation assembly provides a compliant connection between the upper and lower regions of the landing string.

The separation assembly may be configured to define an initial rigid connection, and then a compliant connection upon exposure to the predetermined load, followed by complete separation upon exposure to the same, or a different predetermined load. This arrangement may assist to prevent or minimise the risk of violent separation of the upper and lower landing string regions. Furthermore, this arrangement in which a compliant connection configuration is first established before complete separation may provide time to establish appropriate fluid barriers within the landing string, if required, to minimise any fluid leakage and the like.

The predetermined load may be selected in accordance with operator preference. In some embodiments the predetermined load may be selected to be lower than a defined safety load associated with the remainder of the landing string. Such a safety load may be defined by or be associated with a mechanical limit of proportionality at which permanent deformation within the landing string occurs. Such a safety load may be defined by or be associated with a yield limit. Such a safety load may be defined by or be associated with a load at which one or more joints, connectors, flanges and/or the like begins to separate within the landing string. In some embodiments the predetermined load may be selected to be lower than a failure load associated with the remainder of the landing string. The predetermined load may be selected to be lower than a safety load associated with a vessel, for example handling or lifting equipment mounted on a vessel. For example, the predetermined load may be selected to be lower than the lifting capacity of vessel handling equipment.

The separation assembly may comprise a release arrangement configured to initially secure the upper and lower regions of the landing string together, for example in a rigid manner, and permit or initiate relative movement of said regions upon exposure to the predetermined load. The release arrangement may comprise one or more frangible members which are configured to break and permit relative movement of the upper and lower regions upon exposure to the predetermined load. At least one frangible member may comprise a shearable member, such as a shear pin, shear ring or the like. The release arrangement may comprise a frangible component which directly engages at least one of the upper and lower regions or associated components. The release arrangement may comprise a frangible component which indirectly engages at least one of the upper and lower regions or associated components. For example, a frangible element may engage a retention member, such as a captive ring member or the like.

The release arrangement may be located intermediate the upper and lower region of the landing string. For example, the release arrangement may be located at an interface region between the upper and lower regions of the landing string.

The separation assembly may comprise first and second separable components, wherein the first component is associated with the upper region of the landing string and the second component is associated with the lower region of the landing string. In some embodiments one or both of the first and second separable components may be integrally formed with a respective upper and lower landing string region. In some embodiments one or both of the first and second separable components may be separately formed and connected to a respective upper and lower landing string region, for example via a threaded connection or the like.

The first and second separable components may be secured together to permit connection between the upper and lower regions of the landing string. The first and second components may be rigidly secured together until exposure to the predetermined load. The first and second separable components may be secured together by a release arrangement, such as a frangible release arrangement, for example as defined above.

The first and second separable components may define respective interface regions configured to permit said components to engage each other.

The first and second separable components may be configured to permit a telescoping movement therebetween. This telescoping arrangement may permit relative movement between the upper and lower regions of the landing string while remaining connected together. Such telescoping movement may be permitted by the respective interface regions.

The interface regions may comprise respective interface surfaces configured to engage each other.

One of the first and second separable components may comprise or define a projection which is received within a recess formed within the other of the first and second separable components. The projection may define a cylindrical projection, annular projection or the like, and the recess may correspond. The projection and recess may define tapered surfaces. Such an arrangement may assist in providing a smooth break-away from a rigid connection.

The first and second separable components may be configured to transmit bending between the upper and lower regions of the landing string. One or both of the first and second separable components may comprise one or a plurality of land-out plates, ribs or the like configured to permit transmission of bending.

The landing string may comprise at least one valve assembly. The landing string may comprise a plurality of valve assemblies.

The landing string may comprise a lower valve assembly. The lower valve assembly may be located within the lower region of the landing string. The lower valve assembly may be located adjacent the separation assembly. The lower valve assembly may be configured to isolate the lower region of the landing string, for example following initiation of relative movement between the upper and lower regions of the landing string. The lower valve assembly may comprise or define a sub sea test tree (SSTT).

The landing string may comprise an upper valve assembly. The upper valve assembly may be located within the upper region of the landing string. The upper valve assembly may be located adjacent the separation assembly. The upper valve assembly may be configured to isolate the upper region of the landing string, for example following initiation of relative movement between the upper and lower regions of the landing string. The upper valve assembly may comprise or define a retainer valve.

The separation assembly may be interposed between upper and lower valve assemblies, for example between an upper retainer valve and a lower SSTT.

The landing string may comprise a shear-sub component configured to be sheared by eternal equipment, such as a BOP. The shear sub component may define a separable component of the separation assembly.

The separation assembly may be located in a lower region of the landing string. The separation assembly may be located within a region of the landing string which, in use, is to be located within a BOP.

The separation assembly may permit reconnection following complete separation of the upper and lower regions of the landing string.

The separation assembly may permit a rigid connection to be reinstated following initiation of relative movement between the upper and lower regions of the landing string.

The landing string may be configured for temporary use. The landing string may be retrievable. The landing string may be configured to define or form part of a permanent well infrastructure, such as a completion.

The landing string may be adapted for use in well testing operations, production operations, intervention operations, deployment operations, well kill and abandoning operations or the like, or any suitable combination thereof.

The landing string may be configured for use in an exploration and appraisal well.

The landing string may be configured for use in a production well. The landing string may be configured for use in an injection well.

The landing string assembly may be configured for subsea use. The landing string assembly may be adapted to extend through a riser, such as a marine riser.

The landing string may comprise a plurality of tubular members secured together, for example by end-to-end threaded connections, welded connections or the like.

The landing string may be configured for use in deep water.

The landing string may comprise a tubing hanger arranged to support a tubing string extending into an associated well.

The wellhead assembly may comprise a manifold or the like.

The landing string may comprise a lubricator valve assembly configured to permit the passage of tooling and the like into the landing string.

According to a second aspect of the present invention there is provided a method of controlling load transmission along a landing string, comprising:

-   -   providing a separation assembly between upper and lower regions         of a landing string;     -   configuring the separation assembly to permit relative movement         between the upper and lower regions of the landing string upon         exposure to a predetermined load.

The method may comprise permitting complete separation of the upper and lower regions of the landing string via the separation assembly.

The method according to the second aspect may be performed by use of the landing string according to the first aspect. In this respect features and defined and implied uses of such features presented in relation to the first aspect may apply to the second aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 illustrates a landing string which includes features according to embodiments of aspects of the present invention;

FIG. 2 is a cross-sectional view of a separation assembly of the landing string arrangement of FIG. 1;

FIG. 3 is a cross-sectional view of a portion of a separation assembly of a landing string in accordance with an alternative embodiment of the present invention; and

FIGS. 4A to 4C are cross-sectional illustrations of a separation assembly of a landing string according to a further embodiment of the present invention, showing sequences in operation.

DETAILED DESCRIPTION OF THE DRAWINGS

A landing string 10 is diagrammatically illustrated in FIG. 1, shown in use within a riser 12 and extending between a surface vessel 14 and a subsea wellhead assembly 16 which includes a BOP 18 mounted on a wellhead 20. The use and functionality of landing strings are well known in the art for through-riser deployment of equipment, such as completion architecture, well testing equipment, intervention tooling and the like into a subsea well from a surface vessel.

When in a deployed configuration the landing string 10 extends through the riser 12 and into the BOP 18. While deployed the landing string 10 provides many functions, including permitting the safe deployment of wireline or coiled tubing equipment (not shown) through the landing string 10 and into the well, providing the necessary primary well control barriers and permitting emergency disconnect while isolating both the well and landing string 10.

Wireline or coiled tubing deployment may be facilitated via a lubricator valve 22 which is located proximate the surface vessel 14.

Well control and isolation in the event of an emergency disconnect is provided by a suite of valves which are located at a lower end of the landing string 10 inside the BOP 18. The valve suite includes a lower valve assembly called the subsea test tree (SSTT) 24 which provides a safety barrier to contain well pressure, and also functions to cut any wireline or coiled tubing which extends through the landing string 10. The valve suite also includes an upper valve assembly called the retainer valve 26 which isolates the landing string contents and can be used to vent trapped pressure from between the retainer valve 26 and SSTT 24. A shear sub component 28 extends between the retainer valve 26 and SSTT 24 which is capable of being sheared by shear rams 30 of the BOP 18 if required. In this respect it should be noted that the shear sub component 28 may only be utilised when the landing string is fully deployed and aligned with the BOP shearing rams. A slick joint 32 extends below the SSTT 24 which facilitates engagement with BOP pipe rams 34.

The landing string 10 includes a tubing hanger 36 at its lowermost end which engages with a corresponding tubing hanger 38 provided in the wellhead 20. When the landing string 10 is fully deployed and the corresponding tubing hangers 36, 38 are engaged, the weight of the lower string (such as a completion, workover string or the like which extends into the well and thus not illustrated) becomes supported through the wellhead 20. However, during deployment of the lower string through the riser 12 all the weight and other forces associated with the lower string must be entirely supported through the landing string 10. Furthermore, when deployed a degree of tension is conventionally applied to the landing string 10, for example to prevent adverse compressive forces being applied, for example due to the weight of the landing string 10, which can be significant in deep water.

The landing string 10 must thus be designed to accommodate significant in-service loadings, such as the global weight/tension from a supported lower string. However, in some applications it may be the case that global tension and loading could exceed safety limits, and even failure limits associated with the landing string 10 and components. Furthermore, in some instances the global weight or tension may approach or exceed the safe lifting capacity of handing equipment 40 associated with the vessel 14. The present invention seeks to address such issues by incorporating a separation assembly 42 into the landing string 10 which permits relative movement, specifically axial movement, between an upper region 44 and lower region 46 of the landing string 10 upon exposure to a predetermined load. This relative movement may minimise or eliminate further transmission of load between upper and lower regions 44, 46. In the present embodiment the separation assembly 42 is interposed between the SSTT 24 and retainer valve 26. However, in other embodiments the separation assembly 42 could be located at any location along the landing string.

In some embodiments relative movement permitted by the separation assembly 42 may include complete separation of the upper and lower regions 44, 46. In other embodiments such relative movement may comprise reconfiguring from a rigid connection to a compliant connection between the upper and lower regions 44, 46. In still further embodiments such relative movement may include initial reconfiguring from a rigid connection to a compliant connection, and then to complete separation.

Reference is now made to FIG. 2 in which there is shown a cross sectional view of a separation assembly, generally identified by reference numeral 42 a, in accordance with one embodiment of the present invention. In a similar manner to that described in relation to FIG. 1, the separation assembly 42 a is configured to permit relative movement between an upper region 44 a and a lower region 46 a of a landing string upon exposure to a predetermined load. It will be recognised that the separation assembly 42 a is shown in FIG. 2 in a connected configuration in which a rigid connection between the upper and lower regions 44 a, 46 a of the landing string is present.

The separation assembly 42 a in the illustrated embodiment is intended to be interposed between an upper retainer valve (not shown) and a lower SSTT (also not shown), although other configurations are possible. The separation assembly 42 a comprises upper and lower separable components 48, 50, wherein the upper component 48 forms part of the upper region 44 a of the landing string, and the lower component 50 forms part of the lower region 46 a of the landing string. In the present embodiment the upper component 48 may define or form part of the shear sub 28 shown in FIG. 1. The lower component 50 may form part of the SSTT 24 shown in FIG. 1, or, as in the present case, may define a latch connector which facilitates a latch connection with the SSTT 24.

The upper component 48 defines an annular rib or projection 52 which extends axially from a lower face 54 of the upper component 48 and is received within a complimentary annular recess 56 which extends into an end face 58 of the lower component 50. Although not illustrated, a sealing arrangement may be provided between the end faces 54, 58. A plurality of circumferentially arranged shear pins 60 hold the rib 52 within the recess 56 to establish a rigid connection between the upper and lower components 48, 50. In this arrangement the pins 60 function to transmit loading, particularly tensile loading between the components 48, 50 when connected. Furthermore, the pins 60 are configured to shear upon exposure to a predetermined load, specifically a predetermined axial (in this case tensile) load transmitted along the landing string and through the separation assembly 42 a. Upon shearing of the pins 60 complete separation of the components 48, 50 and thus upper and lower regions 44 a, 46 a of the landing string occurs. This prevents further load transmission across the separation assembly 42 a which may provide a number of benefits. For example, this arrangement may remove the load of the lower region 46 a of the landing string and any supported equipment from the surface vessel 14, such as the surface vessel handling equipment 40 (FIG. 1), preventing its capacity from being exceeded.

The rib 52 and recess 56 define a complimentary tapered profile. Such a profile assists smooth separation of the components 48, 50.

An alternative arrangement of a landing string separation assembly, in this case generally identified by reference numeral 42 b is illustrated in FIG. 3. The separation assembly 42 b is intended to be interposed between an upper retainer valve (not shown) and a lower SSTT (also not shown), although other configurations are possible. The separation assembly 42 b comprises upper and lower separable components 62, 64, wherein the upper component 62 forms part of an upper region 44 b of the landing string, and the lower component 64 forms part of the lower region 46 b of the landing string. In the present embodiment the upper component 62 may define or form part of the shear sub 28 shown in FIG. 1. The lower component 64 may form part of or be connected to the SSTT 24 shown in FIG. 1.

The upper component 62 comprises an upset end 66 which is received within a counterbore 68 formed in the lower component 64. A number of axially arranged circumferential ribs or plates 70 are formed in one or both of the upset end 66 and counterbore 68 to facilitate the transmission of bending across the separation assembly 42 b. A captive ring 72 is secured to the lower component 64 via one or a plurality of shear pins 74 (only one shown), wherein the captive ring 72 and shear pins(s) 74 provide a substantially rigid connection between the upper and lower components 62, 64. The pin(s) 74 is/are configured to shear upon exposure to a predetermined load, specifically a predetermined axial (in this case tensile) load transmitted along the landing string and through the separation assembly 42 b. Upon shearing of the pin(s) 74 complete separation of the components 62, 64 and thus upper and lower regions 44 b, 46 b of the landing string occurs.

A further embodiment of a landing string separation assembly, in this case generally identified by reference numeral 42 c, is shown in FIGS. 4A to 4C, wherein FIGS. 4A to 4C provide sequential illustrations of separation of the separation assembly 42 c.

The separation assembly 42 c comprises upper and lower separable components 82, 84, wherein the upper component 82 forms part of an upper region 44 c of the landing string, and the lower component 84 forms part of the lower region 46 c of the landing string. In the present embodiment the upper component 82 may define or form part of the shear sub 28 shown in FIG. 1. The lower component 84 may form part of or be connected to the SSTT 24 shown in FIG. 1.

The upper component 82 is initially partially located within the lower component 84, as shown in FIG. 4A, and a rigid connection is achieved via a plurality of shear screws 86. Upon exposure to a predetermined tensile load applied through the separation assembly 42 c the shear screws 86 will shear, permitting relative axial telescoping movement of the upper and lower components 82, 84, as shown in FIG. 4B. In this configuration the upper component 82 remains inserted within the lower component 84, prevented from complete release by a captive ring 88, such that a compliant connection between the components 82, 84 is established. Such a compliant connection may provide appropriate time to set in place fluid barriers, such as by actuation of the SSTT 24 and retainer valve 26. Also, such a compliant connection may prevent a violent separation of the upper and lower component 82, 84 from occurring. An annular region 80 defined between the components 82, 84, as shown in FIG. 4A, may comprise a fluid which is ejected via restrictions 92 upon relative movement of the components 82, 84 which may establish a degree of damping.

As shown in FIG. 4B, the captive ring 88 is secured to the lower component 84 via a plurality of shear screws 94 which are configured to shear when a predetermined tensile load is again applied through the assembly 42 c, permitting complete separation of the components 82, 84, as illustrated in FIG. 4C. The shear screws 86 and shear screws 94 may be arranged to shear upon exposure to the same or a different predetermined load.

In the embodiment shown in FIG. 4 the separation assembly 42 c is configured to provide protection against a predetermined tensile load. However, the assembly 42 c may also provide protection against a predetermined compressive load.

It should be understood that the embodiments described herein are merely exemplary and that various modifications may be made thereto without departing form the scope of the present invention. For example, in the various embodiments described above shear screws are used to provide a means of disconnection upon exposure to a predetermined load. However, other arrangements are possible. For example, a rated latching system may be utilised which permit unlatching upon exposure to a predetermined load. Further, a retractable dog arrangement may be utilised. Also, in some embodiments the upper and lower components of the separation assembly may be configured to be re-connected. 

1. A landing string for use in deploying equipment between a surface vessel and a subsea well, comprising a separation assembly for permitting relative movement of upper and lower regions of the landing string upon exposure to a predetermined load.
 2. The landing string according to claim 1, wherein, in use, the separation assembly permits a controlled relative movement of the upper and lower regions of the landing string at or around the predetermined load.
 3. The landing string according to claim 1, wherein controlled relative movement of the upper and lower regions of the landing string controls transmission of load between said regions and along the landing string.
 4. The landing string according to claim 1, wherein the predetermined load comprises a predetermined axial load.
 5. The landing string according to claim 1, wherein the predetermined load comprises a predetermined tensile load.
 6. The landing string according to claim 1, wherein the predetermined load comprises at least one of a compressive load, a torsional load and a pressure induce load.
 7. The landing string according to claim 1, wherein the separation assembly defines a linkage or connection between the upper and lower regions of the landing string.
 8. The landing string according to claim 1, wherein the separation assembly defines a weak link or connection arrangement.
 9. The landing string according to claim 1, wherein the separation assembly defines a rigid connection between the upper and lower regions of the landing string prior to exposure to the predetermined load.
 10. The landing string according to claim 1, wherein the separation assembly permits relative movement between the upper and lower regions upon exposure to the predetermined load while still defining a connection therebetween.
 11. The landing string according to claim 1, wherein the separation assembly defines a compliant connection between the upper and lower regions following exposure to the predetermined load.
 12. The landing string according to claim 11, wherein the compliant connection retains the upper and lower regions of the landing string in general engagement with each other while minimising the load transference between said regions.
 13. The landing string according to claim 1, wherein the separation assembly damps relative movement between the upper and lower regions of the landing string following exposure to the predetermined load.
 14. The landing string according to claim 13, wherein the separation assembly comprises a fluid damping arrangement for damping relative movement between the upper and lower regions of the landing string.
 15. The landing string according to claim 1, wherein the separation assembly permits complete separation of the upper and lower regions of the landing string.
 16. The landing string according to claim 15, wherein the separation assembly permits complete separation of the upper and lower regions from a rigid connection configuration upon exposure to the predetermined load.
 17. The landing string according to claim 15, wherein the separation assembly permits complete separation of the upper and lower regions from a compliant connection configuration upon exposure to a predetermined load.
 18. The landing string according to claim 15, wherein the separation assembly defines an initial rigid connection, and then a compliant connection upon exposure to the predetermined load, followed by complete separation upon exposure to the same, or a different predetermined load.
 19. The landing string according to claim 1, wherein the predetermined load is selected in accordance with operator preference.
 20. The landing string according to claim 1, wherein the predetermined load is selected to be lower than a defined safety load associated with the remainder of the landing string.
 21. The landing string according to claim 1, wherein the predetermined load is selected to be lower than a safety bad associated with a vessel.
 22. The landing string according to claim 1, wherein the separation assembly comprises a release arrangement for initially securing the upper and lower regions of the landing string together and for permitting or initiating relative movement of said regions upon exposure to the predetermined load.
 23. The landing string according to claim 22, wherein the release arrangement comprises one or more frangible members which are configured to break and permit relative movement of the upper and lower regions upon exposure to the predetermined load.
 24. The landing string according to claim 1, wherein the separation assembly comprises first and second separable components, wherein the first component is associated with the upper region of the landing string and the second component is associated with the lower region of the landing string.
 25. The landing string according to claim 24, wherein one or both of the first and second separable components are integrally formed with a respective upper and lower landing string region.
 26. The landing string according to claim 24, wherein one or both of the first and second separable components are separately formed and connected to a respective upper and lower landing string region.
 27. The landing string according to claim 24, wherein the first and second separable components are secured together to permit connection between the upper and lower regions of the landing string.
 28. The landing string according to claim 24, wherein the first and second components are rigidly secured together until exposure to the predetermined load.
 29. The landing string according to claim 24, wherein the first and second separable components are secured together by a release arrangement.
 30. The landing string according to claim 24, wherein the first and second separable components permit a telescoping movement therebetween.
 31. The landing string according to claim 24, wherein one of the first and second separable components comprises or defines a projection which is received within a recess formed within the other of the first and second separable components.
 32. The landing string according to claim 31, wherein the projection and recess define tapered surfaces.
 33. The landing string according to claim 24, wherein the first and second separable components are configured to transmit bending between the upper and lower regions of the landing string.
 34. The landing string according to claim 24, wherein one or both of the first and second separable components comprise one or a plurality of land-out plates or ribs to permit transmission of bending.
 35. The landing string according to claim 1, comprising at least one valve assembly.
 36. The landing string according to claim 1, comprising a lower valve assembly located within the lower region of the landing string.
 37. The landing string according to claim 36, wherein the lower valve assembly comprises or defines a sub sea test tree (SSTT).
 38. The landing string according to claim 1, comprising an upper valve assembly located within the upper region of the landing string.
 39. The landing string according to claim 38, wherein the upper valve assembly comprises or defines a retainer valve.
 40. The landing string according to claim 1, comprising a shear-sub component configured to be sheared by external equipment.
 41. A method for controlling load transmission along a landing string, comprising: providing a separation assembly between upper and lower regions of a landing string; configuring the separation assembly to permit relative movement between the upper and lower regions of the landing string upon exposure to a predetermined load. 